Typically, in an elevator a car is moved by means of a drive and guided at guide rails to different access levels of a building. Traction drives or hydraulic drives serve as the drive. A traction drive is composed at least of a motor, a drive pulley and traction means such as, for example, a cable or belt. The motor drives the drive pulley by way of a shaft. The drive pulley in turn transmits traction to the traction means by way of friction forces. A car and a counterweight, which compensates for the gravitational force of the car, are suspended at the traction means. A hydraulic drive comprises at least one hydraulic cylinder and hydraulic piston. A working fluid, which sets the hydraulic piston into a vertical upward or downward movement depending on the pressure built up, is compressed in the hydraulic cylinder. A car placed on the piston is moved correspondingly.
European Safety Standard EN-81 prescribes the use of a safety brake or a so-called catch brake. Such a safety brake is mounted on the car and in the event of drive failure such as, for example, traction means fracture or rapid pressure drop in the hydraulic cylinder can protect the car from a fatal fall. For that purpose the safety brake is traditionally connected with a mechanical speed limiter. This speed limiter triggers the safety brake in the event of excess speed and the safety brake builds up a braking force at the guide rails and thus brings the car to a safe stop.
In more recent times it has been sought to replace mechanical speed limiters and mechanically triggered safety brakes with electronic speed limiters and electronically triggered safety brakes, which are very reliable, compliance-friendly and economically producible.
Patent specification EP 1 400 476 A1 shows an example of such an electronically triggered safety brake. This safety brake can be triggered by a solenoid activated by the speed limiter and has to be capable of fail-safe actuation. For that reason the safety brake is held by the electric motor in a rest position against a spring-biased lever arm. In the event of power failure the energy feed to the solenoid is interrupted and the energy stored in the spring released. Consequently, the safety brake is triggered. The safety brake shown in EP 1 400 476 A1 is distinguished by high trigger reliability. However, this is accompanied by a solenoid which in a rest state has to be constantly supplied with energy and which has to hold the safety brake in a rest position against a biased spring.